Method of grinding



E. KRAMER IETHOD OF GRINDING Filed June 22. 1929 II l.

UHHU

Feb- 17. v1931.

i Patented Feb. 17, 1931 ERWIN KRAMER, or BERLI GERMANY,

ASSIGNOR TO THE FIRM: HARTSTOFF- METALL A. G., (HAMETAGQ OF BEBLIN-COPENIOK, GERMANY METHOD 0]? Application filed June 22, 1929, Se1'ia1 '.N'o.

My invention relates to a method of grinding; more especially, it relates to a method of grinding, discharging and separating materials or substances down to the finest grades of disintegration, including such as cannot be obtained even with the finest sieves, in fact, even down to colloidal fineness.

It is possible, with the aid of this invention, to produce large amounts also of pul-v ve'rulent metals, including tough and ductile or 'tensible ones, such as copper, wroughtiron and the like, the grain ofsuch powders being comparatively equal, and the dimension or diameter of the particles having a smallness even down to one thousandth of a millimeter, or still less.

The disintegration is effected with the aid of a mill, in which the respective material or substance is reduced to powder by blows. or knocks. The inventionpermits also improved beetling mills to be used in such a way that they produce and deliver powders V of a far smaller fineness than could .be ob ones, these latter being then subjected to another grinding operation.-

the particular feature of the present in 1-. proved method resides therein that the air tained hitherto.-

It is, furthermore, possible to withdraw'or remove adsorbed gases from the material either before the grinding or during the grinding operation. On this account, the further possibility is afforded of effecting that operation 'in a gaseous atmosphere which, otherwise, might be perceptible ina disagreeable manner- Very fine metallic powders, such as very fine pulverulent iron, aluminum, magnesium, and similarmetals,

as is known, will. become ignited spontaneously in the open air when hydrogen has been absorbed by them. I

The basis of the-present invention is theknownprocess of separating the pulverulent material discharged from a-mill, by a sifting operation, into fine particles and coarse f But as compared ith said former process,

current used for carrying the ground material out of the mill to the sifting apparatus does not enter the latter, and that the pressure existing in the sifting apparatus is con- GRINDING 373,049, and in Germany an, 22, 1929;

siderably below the pressure existing in the mill, and that, finally, a gaseous atmosphere can be made use of in the mill other than which is present in the sifting apparatus.

If, for example, the mill is operating under normal atmospheric pressure (which may be increased or decreased to a certain degree by the amount of air required .for carrying the ground material into the sifter), the pressurein the sifter will be considerably below that in the mill, and may approach vacuum, just as suited for the size of the particles to be dealt with. In vacuo all materials, irrespective of their nature and their size, fall, as is known, with equal velocity, and it is, therefore, possible to separate even the most minute particles, but it is not possible to sift them according to the different sizes. .It is with consideration of this fact that the sifter, according to this invention, is always open ating under a generally considerably reduced pressure whereby it, is rendered possible to sift even extraordinarily fine particles; Be-

sides, the fineness of the sifting can be influenced materially by the amount of the reduced pressure being changed or varied, and besides, the .gasfilms adhering to the fine particles of the disintegrated material leave the respective-particles and can be removed powder can be mixed with, or exposed to the action of, an inert gas, as will be more fully described hereinafter.

I am aware of the fact that attempts have already been made to carry out the grinding in a beetling mill in vacuo and to separate the powdered product, but in those cases it wasneccssar'y to keepthe entire mill, with all its accessories, under the reduced pressure,

" and that provedto be so difiicult and impractica'ble that further trials were abandoned.

With the'present improvedmethod, however, the mill operates under atmospheric pressure or practically so, the small difference caused by the discharging aircurrentbeing immaterial, and it is by no means difficult to tighten or pack the mill even if it is lou running at high speed. But the sifter which, by the way, does not require much power and the rotary members of which run with a small number of revolutions must, and can, be securely ti htened or packed to exclude from it the outer excess pressure. This need not be done with the mill proper and its accessories proper, and these parts need not, therefore, be constructed correspondingly strong so as to be able to stand a certain strong excess pressure. Only the sifter must be constructed in this manner.

The fineness of grinding of the mill can be considerably increased by the elimination of disturbances produced in the mill by the atmosphere, while this aim has already been attempted by the mill grinding in vacuo. The

. same result, at least in a more satisfying degree, is attained by the use, in the mill, of a comparatively light gas, such as hydrogen or helium or, although in a lesser degree, illuminating gas. The fine particles absorb, it is true, somewhat large amounts of said gases, but these amounts are removed and eliminated in the sifter by reason of the greatly reduced pressure therein. Thus, the invention permits the advantageous properties of the light gases to be utilized without any danger of any detrimental consequences resulting from the use of said gases.

By the reduced pressure being employed solely in the sifter, and being kept apart from the air-current used for discharging the particles from the mill, the reduced pressure can be continually maintained without a particularly large vacuum pump, etc., for that purpose being required. Only the small amounts of gas escaping from the pulverulent particlesneed be sucked away, and also such small amounts as may enter into the sifter through leakages. The high dilution or rarefaction of the air in the sifter serves at the same time as a protection against oxidation of the ground material, and against dust explosions as frequently occur under other circumstances.

Of course the sifter can also be filled with inert gases if these are suitably diluted or rarefied. In this case, even hydrogen can be used, as in most cases the amounts of hydrogen adhering to the particles are too small to act detrimentally. I Any possible, although improbable, danger can be obviated still more effectively by the powder, after having been sifted, but prior to its removal from the sifter, being washed with an inert gas of a higher pressure than that which existed in the sifter. The powder which is under pressure sucks up, of course, the respective amounts of. gas very eagerly so that the very small amount of hydrogen which is already diluted to a considerable degree will be still further diluted orrarefied.

In order to carry out my invention I em- 1,793,oos

ploy a plant as shown diagrammatically and by way of example on the accompanying drawing on which that plant is shown in side-view. On this drawing 1 denotes the mill which is supplied with the material to be disintegrated and pulverized from the receptacle 2 through the rotary valve-cross 3. This valve is connected with the inlet branch 7 of the mill by a leg 4 of a threepart member 4, 5, 6, the legs 4 and 6 of which may be termed branches, whereas the leg 5 is, in fact, a tube. This tube connects the mill with a blower 9. The disintegrated material is carried away, and out of the mill, into the sifter 11 by the current of air flowing from the inlet branch 7 through the mill to the outlet branch 8, and then through the tube 10 which connects the mill with the sifter 11. This apparatus 11 is, however, more in the nature of a separator in which the ground material is separated from the air, the latter flowing back to the blower 9 through the pipe 12, whereas the pulverulent material passes through a valve or shutof cook 13 into an intermediate receiver 14, at the lower end of which is again a valve or a shut-off cock 15 by the casing of which the receiver 14 is connected with a conveying tube 17 in which a conveying screw 16 is housed. The tube 17 extends into the sifter proper 18 which is designed, in the constructional form selected as an example, as a so-called rising sifter. It consists of a sheet-metal cylinder 19 which is closed at its bottom, as well as at its top, and in which the powder is stirred and blown up wardly, the height to whieh'the particles rise depending upon their size or weight. When the particles again sink they are intercepted at several different heights, as is more fully described hereinafter.

The pulverulent material entering into the tube 17 from the receptacle 14 through the cook 15 is conveyed into the sifter 18 by means of the screw 16 and drops to the bottom 21 of the casing 19 containing a horizontal rotary brush 22 that is affixed to a vertical shaft 20 driven by an electromotor 40 housed in a casing 41 supported on the top of the casing 19. The particles being stirred by the rotating brush rise; they rise to a greater height, the smaller or lighter they are; those of the upwardly whirled particles which contact with the inner sur face of the cylinder 19 are guided thereby into the circular gutters 23, 24 and 25, of which 23 receives the finest particles, 25

the coarse particles, and 24: particles of treated a second time. This re-conduction is effected in two stages in order to pervent any communication between the sifter and the mill. First the valve 27 is opened so that the coarse particles passinto the receiver 28. Then the valve 27 is closed and the valve 29 is opened so that said particles pass from the appertaining members are of like construction, I have shown only that connected with the tube 31, viz. the receiver 33 which is connected with said tube through a Valve 32 and has at its lower end a valve 34 by the casing of which the receiver 33 can be connected with a transport vessel 35. In this manner the pulverulent product can be removed from the sifter during operation, in that the cooks 32 and 34 are opened and closed in alternation, just as has been described with respect to the cooks 27 and 29, the casing or vessel 33 serving as intermediate receiver.

It is possible to aerate the powder in the vessel 33 prior to being discharged therefrom, there being provided at it a cook 36 for that purpose. Also an inert gas, as for instance nitrogen, carbonic acid or the like, can be introduced into the receiver 33 through the cock 36 so that the powder becomes saturated with the respective gas before being discharged into the transport vessel 35. Of course the cock 32 is kept closed during that time.

In order to provide for a continuous and thorough emptying of the gutters 23 and 24,

as well as 25, rotary arms 37, 38 and 39 are attached to the shaft 20 for pushing the powder toward the discharge opening. Shaft 20 is. operated by a small electromotor contained in a closed casing 41.

The reduced pressure in the sifter can be watched at a gauge 42 provided on the top of the casing 19, or on the conical cover 43 thereof, from which a pipe 44, 45 leads to a vacuum pump 46.

The sifter is also connected by pipe 44 with a dust-filter 47 comprising a filter-cloth 48 and a casing 47, said cloth dividing said casing into two chambers. The pipe 44 is connected with one of said chambers, and the other chamber is connected by a pipe 45 with a vacuum pump 46. The gas sucked out of the sitting casing by said pump 46 must, thus, pass through the filter cloth by which particles of the ground material carried along, perhaps, with and by the gas current are intercepted. Such intercepted and collected par and so on.

ticles may be withdrawn into a vessel 49, if desired with the insertion of an intermediate receiver and two alternately operated cocks, as described in connection with the vessels 28 and 33. The same manner of operation is carried out when the material is conveyed from the separator 11 to the sitter 18, viz. with the aid of the cooks or valves 13 and 15 and the intermediate vessel 14.

The dimensions of these three intermediate vessels 14, 28 and 33 are such that the small amounts of gas passing through them together with the respective amounts of the pulverulent material cannot have any detrimental influence. A particularly practical manner of operation, as regards the entire plant, is this that when any one of the said inter mediate vessels has been used in the manner described, the rotary stirring member 22 is brought to standstill until the gauge 42 indicates again a uniform reduced pressure. The several shut'oif cocks or valvesmay be manually operated, but it is of course possible to effect that mechanically by means of a suitably designed control device, for instance by 'means of a control drum or the like.

I wish it to be understood that I do not limit myself to the details shown in the drawing and herein described since many variations may be made without a departure from the essence of this invention. The object of the construction as shown is to eliminate as much as possible intermediate conveying op-' eration and manual labor, but itdepends upon the available space and other conditions of any given case whether or not intermediate conveying operation and manual work can more or less be dispensed with. This is true of the position of the sifter with respect to the separator, as well as with respect to the position of the mill with respect to the sifter,

The separator shown in the drawing is of the so-called cyclone type, but separators of other types may be used, and also sifters of another type than that shown may be employed.

The invention is particularly suitable in connection with mills of the kind, in which the disintegration of the material is effected by blows and shocks, or the like, as in beetling mills and the like, the fact being that by combining such mills with parts arranged as described, that is to say, by operating a plant of this kind according to the present method the degree of fineness of the product can be considerably increased. With ordinary beetling mills and the like there is, in the course of operation, reached a point beyond which no greater fineness of the product can be attained, but by the present improved method such result can be'attained without any particular difiiculty. There is, thus, attained a far finer and better product, the output is considerably increased, and the efliciency of the plant, as well as the economy of operation,

are greatly improved.

I l. The method of sifting powdered material comprising conveying the material in a gas at one pressure, separating it therefrom, and then classifying it in a closed space containing a gas at different pressure.

2. The method of sifting powdered material comprising conveying the materialin a gas at one pressure, separating it therefrom, and then stirring it in a closed space containing a gas at different pressure.

3. The method of sitting powdered material comprising conveying the material in a gas at one pressure, separating it therefrom, and stirring it in a' closed space containing a gas at reduced pressure, causing the material to settle at different levels.

4. The method of sifting powdered material comprising conveying the material in a gas at one pressure, separating it therefrom, conveying it to a closed chamber containing a gas at reduced pressure approaching vacuum and stirring it in said chamber causing it to settle at difierent levels.

5. The method as specified in claim 1, in which the gas in said closed space is an inert gas li hter than air.

6. Th combination with a disintegrator; a closed chamber, a separator intermediate said chamber and said disintegrator, means for conveying the disintegrated material from said disintegratorto said separator, means for conveying the material from said separator to said closed chamber, means for maintaining in said chamber a reduced pressure, means for causing said material to rise in said closed chamber causing it to settle at difierent levels in said chamber, and means for discharging the material from the diflierent levels of said chamber.

7. The combination as specified in claim 6,

including means for controlling the discharge of the material from the difierent levels of said chamber without disturbing the pressure maintained in said chamber.

In testimony whereof I afiix my signature.

ERWIN KRAMER. 

